Shock detecting device
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a shock detecting device; and more particularly, to a shock detecting device which mechanically ignites without electricity an ignition element for use as a starting sensor of an anti-shock safety system, such as an air-bag or a seatbelt tensioner, for example. 
     2. Description of Related Art 
     A conventional shock detecting device of the above type, is disclosed in Japanese Patent Laid Open No. 60 (1985) -248456. In this publication, the movement of a sensing weight causes a rod to be depressed and rotated against an urging force. The rotation of the rod in turn rotates a rotatable shaft. Disengagement of an ignition pin upon rotation of the rotatable shaft permits the ignition pin to be moved by an urging force of a spring. 
     However, in the above-mentioned publication the ignition pin engages and disengages the shaft by the rotation thereof, so that the rotatable shaft and the ignition pin engage each other at one side. Accordingly, the ignition pin is supported slightly inclined during movement because of the urging force of the spring. After the ignition pin disengages the rotatable shaft, a smooth sliding of the ignition pin is not obtained, because the ignition pin interacts with or touches the housing during movement. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to reliably and stably maintain a firing lever of a shock detecting device in a cocked rotational position. 
     It is another object of the present invention to obtain a smooth rotational operation of the firing lever in response to a shock condition. 
     It is further an object of the present invention to securely maintain engagement of the firing lever and a cam portion of the shock detecting device in the absence of external shock. 
     Additional objects on advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the inventions. 
     To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the shock detecting device of the present invention comprises, a housing; a firing lever pivotably mounted in the housing to rotate in a first direction from a cocked to a fired position; a weight including a cam rotatably and slidably mounted in the housing, the cam engaging the firing lever when in a cocked position and disengaging the firing lever to permit rotation of the firing lever to the fired position in response to the rotation and sliding of the weight in response to an external shock; and urging means interposed between the firing lever and the housing for constantly urging rotation of the firing lever in the first direction to the fired position. 
     When the firing lever is in engagement with the cam portion of the weight, the position of the firing lever relative the cam is maintained. Therefore, the firing lever is stable in the cocked position, and after disengagement of the firing lever and the cam, the firing lever is not interfaced or in contact with the housing. Accordingly, smooth rotation of the firing lever in the first direction to the fired position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view in partial cut-away form to show a portion of the interior of a shock detecting device constructed according to the present invention; 
     FIG. 2 shows a sectional view in elevation of the shock detecting device of FIG. 1; 
     FIG. 3 is a view similar to FIG. 2, illustrating the position of the cam portion and the firing lever just prior to the disengagement of the cam portion and the firing lever of the device of the present invention; and 
     FIG. 4 is a view similar to FIG. 3 illustrating the position of the cam portion and the firing lever of the device of the present invention after disengagement of the firing lever and the cam portion. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in FIGS. 1 to 4, a weight 2 is disposed within a housing 1. Weight 2 is provided with a pair of spaced circular plate shape portions 2a of large diameter. Weight 2 has a cam portion 2b formed between the large diameter circular plate shaped portions 2a. Weight 2 has concentrically disposed pinion gear portions 2c formed on an outside radial surface of each of the large diameter circular plates 2a, and concentrically disposed shaft portions 2d formed on an outer radial surface of each of the pinion gear portions 2c. Housing 1 has spaced oppositely disposed and aligned linear grooves 1a into which respective shaft portions 2d of weight 1 slidably fit. Rack gear portions 1b are disposed within housing 1 so as to fixedly mesh with respective pinion gears 2c. The grooves 1a, into which the ends of shaft 2d slidably fit are aligned with rack gears 1b. Therefore, weight 2 is rotatably and slidably supported in the grooves 1a of housing 1. Rack gears 1b may be integrally formed as a single unitary structure with housing 1, or fixedly attached to the housing by means such as welding, for example. 
     As heretofore mentioned, weight 2 is provided with larger diameter circular plates 2a, so that the moment of inertia is enlarged, and the weight becomes difficult to actuate in response to very short time shocks, which may occur while traveling over a rough road, or the like. Thus, false operation of the shock detecting device is prevented. Further, actuation can be made to occur as required, because of a particular shape of weight 2. However, this requires not only manufacturing accuracy, but also special material characteristic, so that actuation does not change because of temperature change; making it difficult to obtain stability of performance. 
     Firing lever 3 is rotatably supported within housing 1 by a pin 4. Disposed on opposite sides of the firing lever are a pair of axially spaced weight members. A firing pin 3a is formed at a top end portion of the firing lever 3 and strikes a detonating chamber 5 in response to rotation of firing lever 3. Firing lever 3 is provided with an engaging edge portion 3b which normally engages cam 2b; and the rotation of the firing lever 3 about pin 4 is prevented by engagement of the cam 2b with the engaging edge portion 3b of firing lever 3. Hook portions 1c, and 3c are formed on the housing 1 and the firing lever 3 respectively. Firing lever 3 is constantly urged by a spring 6 interposed between hook portions 1c and 3c in a direction so that its firing pin 3 strikes detonating chamber 5. Therefore, spring 6 maintains both the position of the weight 2 in the housing, and provides the rotational urging force of the firing lever 3 after disengagement of cam portion 2b with engaging edge portion 3b. 
     As above mentioned, firing lever 3 is supported in a cocked condition by pin 4 and cam 2b of weight 2; that is, it is balanced or stabilized between weight 2, namely, the dead load of weight 2, and the urging force of spring 6 between spaced opposing sides of weight 2 upon engagement of the cam 2b and the engaging edge portion 3b of the firing lever. Accordingly, firing lever 3 is supported with stability against the rotational movement or location, and the firing lever 3 does not interact or touch the housing 1 upon the rotation of the lever disengagement of cam 2b and engaging edge portion 3b. As a result, smooth rotation of firing lever 3 is obtained. 
     Two sets of the shock detecting device are preferably provided so as to have point symmetry, and to permit equalization of an input of the inertia load upon assembling on a steering handle pad, etc. This redundancy therefore improves the operation in an optimum manner. 
     In case shock is applied from a direction as shown in FIG. 2, movement of shaft 2d is guided by grooves 1a. As shown in FIG. 3, the meshing of pinion gears 2c with a respective rack gear 1b causes weight 2, and cam 2b to rotate while sliding in grooves 1a in response to the inertia force of the external shock. Disengagement of cam 2b and the engaging edge portion 3b of the firing lever occurs in response to the rotation and sliding of weight 2, along rack gears 1b as shown in FIG. 4. Accordingly, the firing lever 3 rotates on axis pin 4 in response to the urging force of spring 6, and firing pin 3a strikes detonating chamber 5. 
     As above mentioned, engagement between cam 2b and the engaging edge portion 3b is released by the rotational sliding of the weight. Thus, the length of the engaging surface of cam 2b with the engaging edge portion 3b, or in other words, the linear distance weight 2 must rotatably travel in groove 1a can be adjusted to the optimum extent. Accordingly, the engagement between cam 2b and the engaging edge portion 3b can be reliably maintained, and disengagement of cam 2b and engaging edge portion 3b does not occur, because of vibration, to falsely cause release of the firing lever or fail to operate in response to a proper shock. 
     In summary, and according to the present invention, the shock detecting device comprises the housing 1, with weight 2 disposed within housing 1 mounted to rotatably slide in response to an external shock, firing lever 3 is mounted to rotatably pivot about housing 1, cam portion 2b has a semicircular shape formed on weight 2 which is engaged with or disengaged from firing lever 3 in accordance with the rotational sliding of weight 2, and spring 6 is interposed between the housing 1 and firing lever 3 for urging constantly the firing lever in the rotatable direction. 
     With the above-described construction, firing lever 3 can be reliably held in cocked position without slipping, and firing lever 3 is prevented from interacting or touching the housing 1 during rotation of firing lever 3 after disengagement, thereby obtaining a smooth operation of the firing lever. Further, disengagement between cam portion 2b and firing lever 3 occurs upon the rotational sliding of weight 2. Thus, the distance that weight 2 travels while in engagement with cam 2b can be adjusted over a large range to maintain a reliable engaging state. As a result, disengagement between cam 2b and firing lever 3 generated by the vibration can be prevented, as well as the failure to operate because of vibration, also can be prevented. 
     While a particular embodiment of the invention has been shown and described, it will be obvious to those skilled in the art that the various changes and modifications may be made without departing from the invention in its broader aspects and the appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.